It is very well-known that thiodiethanol, by virtue of having hydroxyl groups attached to carbon atoms situated beta to a sulfur atom in an aliphatic chain, exhibits unusual reaction activity. Unlike alkanediols, e.g., 1,4-butanediol, thiodiethanol quite readily undergoes an auto-condensation reaction under the influence of heat and certain acidic dehydration catalysts, such as hydrogen chloride. This was shown by Ballard, et al., U.S. Pat. No. 2,484,369. Low molecular weight, rubber-like materials, as indicated in the following reaction scheme, were obtained: ##STR1##
Woodward et al, J. Poly. Sci. 41,219-223; 225-230; and 231-239 (1959) studied the acid catalyzed auto-condensation of thiodiethanol with hydrochloric acid and phosphorus pentoxide, and the co-condensation with other aliphatic hydroxyl compounds. Hydrochloric acid catalyst provided low-molecular-weight, waxy, water-soluble polymers and ring-closed byproducts, e.g., thioxane and dithiane, while phosphorus pentoxide catalyst afforded products ranging from viscous liquids to rubbery waxes. Some indication of co-condensation with diethylene glycol, trimethylene glycol, and butylene glycols was found. However, no useful rubbery products were produced.
Thiodiethanol has also been copolymerized with equimolar amounts of 1,4-butylene glycol and/or 1,6-hexanediol, in the presence of p-toluenesulfonic acid catalyst to give waxy or low odor polymers (Holtschmidt, U.S. Pat. No. 2,998,413; Schwarz et al U.S. Pat. No. 2,844,566); with triethylene glycol, 1,6-hexanediol and trimethylolpropane in the presence of phosphorous acid catalyst to give low-molecular-weight polymers useful as polyurethane intermediates (Holtschmidt, French Pat. No. 1,373,471) and with thiodipropionic acid catalyst to give hydroxyl-terminated, low-molecular-weight polymers suitable for polyurethanes (Holtschmidt, German Pat. No. 1,045,;641). These products have been reacted with aromatic diisocyanates to provide polyurethane elastomers; see, for example, U.S. Pat. No. 2,862,962; French Pat. No. 1,373,471; German Pat. Nos. 1,007,502; 1,045,641; and 1,108,903; and British Pat. Nos. 791,854 and 818,359.
Sulfur-vulcanizable elastomers, based on the condensation of thiodiethanol with one or more aliphatic diols containing a sulfur-vulcanizable double bond, are described by Aloia, U.S. Pat. No. 3,951,927; Chang et al, U.S. Pat. No. 3,985,708; Chang, U.S. Pat. No. 4,000,213; and Li et al, U.S. Pat. No. 4,028,305, all of which are hereby incorporated herein by reference.
A majority of the known elastomers of polythiodiethanol derived by an acid catalyzed condensation are, to a greater or lesser degree, malodorous. This odor, which can be quite repugnant, is believed to be attributable to the ring closed by-products, thioxane and dithiane, produced during the condensation. The degree of ring closed by-product formation can be reduced to some extent by a prudent choice of acid catalyst, phosphorous acid being one of the best in this respect. However, in any case, useful rubbery products, exhibiting outstanding physical properties, are obtained from thiodiethanol, as described in the aforementioned patents, but these products have not achieved more than limited success in the marketplace because of their characteristic malodor.